Acoustic signature of flow from a fractured wellbore
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Copyright 2015, Society of Petroleum Engineers. Distributed acoustic sensing (DAS) technology is emerging in the area of hydraulic fracture monitoring and diagnosis. The number of applications using DAS technology has been growing significantly from determining flow distribution to detecting multiphase flow. Some of the current DAS technology in the hydraulic fracture diagnosis area utilizes sound intensity on the spectrogram plot of the acoustic measurements to qualitatively analyze fracture initiation. In this paper, we present the results of our simulated fracture, perforation tunnel, and wellbore system experiments measured by a distributed hydrophone array in both the time and frequency domain. The experiments were conducted on a wellbore with two fracture cells. The wellbore can be either horizontal or vertical. The customized fracture cells with long and thin geometry were connected through a perforation tunnel to a 5-inch ID wellbore. In the horizontal wellbore setup, fluid was injected through the fracture cells and perforation tunnels to the wellbore. The experiments used hydrophone and microphone array to measure the acoustic signals from each fracture. Relative locations of the hydrophones to the fractures and the rate difference from the two fractures are the main parameters examined during the experiments. The measured acoustic data were analyzed using DSP techniques to characterize the location and rate differences. We first studied how the fracture and perforation tunnel alone affect the acoustic signature of the flow from the fracture to the wellbore; this study allows extraction of individual fracture and perforation related information from the overall measured DAS data from the combined system. We then analyzed how multiple perforation tunnels and different flow distributions changed the acoustic frequency spectrum. Additional parameters affecting acoustic behavior were investigated including single phase liquid, multiphase fluid, and liquid column. The digital signal processing (DSP) algorithm is explained in the paper. A correlation based on experimental observation was developed to quantitatively estimate the flow rate and flow distribution of multiple perforation tunnels from acoustic signals measured in the wellbore.
